The invention relates to receptors that bind toxins from Bacillus; thuringiensis and thus to pesticides and pest resistance. More particularly, the invention concerns recombinantly produced receptors that bind BT toxin and to their use in assays for improved pesticides, as well as in mediation of cell and tissue destruction, dissociation, dispersion, cell-to-cell association, and changes in morphology.
It has long been recognized that the bacterium Bacillus thuringiensis (BT) produces bacteriocidal proteins that are toxic to a limited range of insects, mostly in the orders Lepidoptera, Coleoptera and Diptera. Advantage has been taken of these toxins in controlling pests, mostly by applying bacteria to plants or transforming plants themselves so that they generate the toxins by virtue of their transgenic character. The toxins themselves are glycoprotein products of the cry gene as described by Hxc3x6fte, H. et al. Microbiol Rev (1989) 53:242. It has been established that the toxins function in the brush-border of the insect midgut epithelial cells as described by Gill, S. S. et al. Annu Rev Entomol (1992) 37:615. Specific binding of BT toxins to midgut brush border membrane vesicles has been reported by Hofmann, C. et al. Proc Natl Acad Sci USA (1988) 85:7844; Van Rie, J. et al. Eur J Biochem (1989) 186:239; and Van Rie, J. et al. Appl Environ Michrobiol (1990) 56:1378.
Presumably, the toxins generated by BT exert their effects by some kind of interaction with receptors in the midgut. The purification of a particular receptor from Manduca sexta was reported by the present inventors in an article by Vadlamudi, R. K. et al. J Biol Chem (1993) 268:12334. In this report, the receptor protein was isolated by immunoprecipitating toxin-binding protein complexes with toxin-specific antisera and separating the complexes by SDS-PAGE followed by electroelution. However, to date, there has been no structural information concerning any insect receptor which binds BT toxin, nor have, to applicants""knowledge, any genes encoding these receptors been recovered.
The invention provides recombinant materials for the production of BT toxin-binding receptors as well as methods to employ these materials to generate receptors for use in screening assays for candidate pesticides. Since the native cDNA sequence encoding this receptor, designated BT-R1, has been retrieved-from the tobacco hornworm, encoding DNA for receptors in other species of insects, as well as in other organisms, which have homology to hornworm receptor can be obtained.
Thus, in one aspect, the invention is directed to a polynucleotide in purified and isolated form which comprises a nucleotide sequence encoding a receptor that binds a BT toxin and other ligands and which has the requisite homology to the BT-R1 protein.
In other aspects, the invention is directed to expression systems for nucleotide sequences encoding the receptor, to methods of producing the receptor recombinantly, to the receptor as thus produced, to antibodies specifically immunoreactive with the receptor, to assay methods useful for screening candidate pesticides, to antisense polynucleotides corresponding to the coding sequence, to methods of targeting tissues and/or cells using the binding characteristics of the receptor, and to methods of manipulating tissues and/or cells using the function of the receptor.